AbstractIn‐based halides always present low photoluminescence quantum yield (PLQY) because of poor absorption, limiting their potential applications in luminescence‐related fields. In this work, zero‐dimensional MA₄InCl₇ [MA⁺: CH₃NH₃⁺] halides with different Sb³⁺ doping level are prepared through solvent evaporating method. The Sb³⁺‐doped MA₄InCl₇ shows a broadband yellow emission with full width at half‐maximum of 180 nm and a high PLQY of 84%. Such broadband emission originates from the self‐trapped excitons demonstrated by experimental results and theoretical calculations. Additionally, the Sb³⁺‐doped MA₄InCl₇ is further employed to fabricate white‐light‐emitting diodes, which possesses high color rendering index of 91 and excellent operating stability up to 400 h. Moreover, flexible Sb³⁺‐doped MA₄InCl₇ films are also prepared as x‐ray scintillators, exhibiting low detection limit of 63.3 nGy_air/s and high spatial resolution of 10.0 lp/mm. Thus, this work provides guidance to design perovskite‐based devices with bright luminescence and x‐ray detection with excellent flexibility.image